In modern facilities for manufacturing electronic products such as semiconductor devices and electronic systems, contact probe heads carrying a large number of contact probes and carried by a robot hand are widely used for inspecting electric performance of such electronic products by electrically accessing a large number of points of such electronic products. These contact probes are required to be extremely densely arranged so as to be able to access a large number of points of an extremely small electronic device.
FIG. 7 shows a conventional contact probe. In this contact probe 23, a tubular holder 21 is passed through and fixedly secured to a base board 22, and the tubular holder 23 receives a needle member 24 therein. A lower part or a rear part of the tubular holder 23 is crimped inwards so as to define a small diameter portion or an annular shoulder 27 which cooperates with a reduced diameter portion 28 provided in a middle part of the needle member 24 to restrict the range over which the needle member 24 can move. The front end of the needle member 24 projects from an end of the tubular holder 23, and a coil spring 25 is interposed between the rear end of the needle member 24 and the other end of the tubular holder 23 which is also crimped inwards. The upper end or the rear end of the tubular holder 23 is connected to a lead wire 26 leading to a testing circuit not shown in the drawing.
According to this prior art contact probe 21, since the compression coil spring 25 is disposed in series with the needle member 24, the overall diameter of the contact probe 21 can be minimized. However, since the length of the compression coil spring 25 is relatively small for a given length of the contact probe 21, the biasing force of the needle member 24 changes significantly as the needle member 24 is displaced. Also, to obtain a sufficient biasing force, the wire diameter and the coil diameter of the compression coil spring 25 must be increased, and this offsets the achieved reduction in the outer diameter of the contact probe.
Furthermore, the needle member is desired to be made of hard material such as tungsten or tungsten alloys, but such materials are often unsuitable for machining. Therefore, provision of a small diameter portion 28 in the needle member 24 could present a manufacturing problem.
Generally speaking, to achieve a high density, the structure of each contact probe is desired to be as simple as possible. Further, in order to control the contact pressure of such a contact probe, it is desired to increase the stroke of the contact member for a given length of the contact probe.
In some applications which require elimination of spurious noises, the contact member needs to be shielded over its entire length. This requirement tends to increase the complexity of the contact probe, and, hence, the dimensions of the contact probe.